As the title states.

From my limited research (that produced conflicting results), it seems the arquebus was the standard infantry firearm of its day and muskets were heavier weapons meant to be fired from a rest. At some point, muskets became lighter and they replaced the arquebus.


If the musket was made lighter, wouldn't it be classified as an arquebus? Why the terminology change? Are there other differences besides the weight between the two?

You are asking us why a name changed over a period of a couple hundred years a couple hundred years ago?

I really don't have a clue.  Names or nomenclature sometimes changes over time.  Look at the terms Clip and Magazine. or the Phrase "Lock and Load" vs "Load and Lock"

Apparently "muskets" didn't become "arquebuses" because both were simultaneously morphing into lighter, handier weapons, and the troops armed with them didn't change designations or (at least initially) roles. Armies have always been traditionalists, fairly resistant to change.  

Somewhat similar, perhaps, to the U.S. Army changing weapons from a "rifle" (Garand) to what would have been called a "carbine" (M-16), yet still calling the weapon a "rifle" and the troops armed with it remaining Riflemen instead of becoming Carbineers.  

Perhaps this will shed some light:
arquebus v. musket

The difference?
6 points on a Scrabble Board.